Method and apparatus for selecting a carrier in a wireless communication system

ABSTRACT

A method and apparatus for selecting a carrier in a wireless communication system is provided. a pico eNodeB (eNB) transmits a carrier information request message including a request of information on carriers used by a macro eNB, receives a carrier information response message as a response of the carrier information request message, the carrier information response message including the information on carriers used by the macro eNB, and selects a primary cell (PCell) of the pico eNB based on the received information on carriers used by the macro eNB.

This application is a 35 USC §371 National Stage entry of InternationalApplication No. PCT/KR2012/005835 filed on Jul. 20, 2012, and claimspriority of U.S. Provisional Application No. 61/509,585 filed on Jul.20, 2011, each of which is hereby incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communication, and moreparticularly, to a method and apparatus for selecting a carrier in awireless communication system.

2. Related Art

Universal mobile telecommunications system (UMTS) is a 3rd generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3GPP LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

FIG. 1 shows network structure of an evolved universal mobiletelecommunication system (E-UMTS). The E-UMTS may be also referred to asan LTE system. The communication network is widely deployed to provide avariety of communication services such as voice over internet protocol(VoIP) through IMS and packet data.

As illustrated in FIG. 1, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an evolved packet core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNB) 20, and a plurality of user equipment (UE) 10. Oneor more E-UTRAN mobility management entity (MME)/system architectureevolution (SAE) gateways (S-GW) 30 may be positioned at the end of thenetwork and connected to an external network.

As used herein, “downlink” refers to communication from eNB 20 to UE 10,and “uplink” refers to communication from the UE to an eNB. UE 10 refersto communication equipment carried by a user and may be also referred toas a mobile station (MS), a user terminal (UT), a subscriber station(SS) or a wireless device.

An eNB 20 provides end points of a user plane and a control plane to theUE 10. MME/S-GW 30 provides an end point of a session and mobilitymanagement function for UE 10. The eNB and MME/S-GW may be connected viaan S1 interface.

The eNB 20 is generally a fixed station that communicates with a UE 10,and may also be referred to as a base station (BS) or an access point.One eNB 20 may be deployed per cell. An interface for transmitting usertraffic or control traffic may be used between eNBs 20.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, Inter core network (CN) node signaling for mobilitybetween 3GPP access networks, Idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), packet data network (PDN)GW and serving GW selection, MME selection for handovers with MMEchange, serving GPRS support node (SGSN) selection for handovers to 2Gor 3G 3GPP access networks, roaming, authentication, bearer managementfunctions including dedicated bearer establishment, support for publicwarning system (PWS) (which includes earthquake and tsunami warningsystem (ETWS) and commercial mobile alert system (CMAS)) messagetransmission. The S-GW host provides assorted functions includingper-user based packet filtering (by e.g. deep packet inspection), lawfulinterception, UE internet protocol (IP) address allocation, transportlevel packet marking in the downlink, UL and DL service level charging,gating and rate enforcement, DL rate enforcement based on APN-AMBR. Forclarity MME/S-GW 30 will be referred to herein simply as a “gateway,”but it is understood that this entity includes both an MME and an SAEgateway.

A plurality of nodes may be connected between eNB 20 and gateway 30 viathe S1 interface. The eNBs 20 may be connected to each other via an X2interface and neighboring eNBs may have a meshed network structure thathas the X2 interface.

FIG. 2 shows architecture of a typical E-UTRAN and a typical EPC.

As illustrated, eNB 20 may perform functions of selection for gateway30, routing toward the gateway during a radio resource control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of broadcast channel (BCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE_IDLE state management,ciphering of the user plane, SAE bearer control, and ciphering andintegrity protection of NAS signaling.

FIG. 3 shows a user-plane protocol and a control-plane protocol stackfor the E-UMTS.

FIG. 3(a) is block diagram depicting the user-plane protocol, and FIG.3(b) is block diagram depicting the control-plane protocol. Asillustrated, the protocol layers may be divided into a first layer (L1),a second layer (L2) and a third layer (L3) based upon the three lowerlayers of an open system interconnection (OSI) standard model that iswell known in the art of communication systems.

The physical layer, the L1, provides an information transmission serviceto an upper layer by using a physical channel. The physical layer isconnected with a medium access control (MAC) layer located at a higherlevel through a transport channel, and data between the MAC layer andthe physical layer is transferred via the transport channel. Betweendifferent physical layers, namely, between physical layers of atransmission side and a reception side, data is transferred via thephysical channel.

The MAC layer of the L2 provides services to a radio link control (RLC)layer (which is a higher layer) via a logical channel. The RLC layer ofthe L2 supports the transmission of data with reliability. It should benoted that the RLC layer illustrated in FIGS. 3(a) and 3(b) is depictedbecause if the RLC functions are implemented in and performed by the MAClayer, the RLC layer itself is not required. A packet data convergenceprotocol (PDCP) layer of the L2 performs a header compression functionthat reduces unnecessary control information such that data beingtransmitted by employing IP packets, such as IPv4 or IPv6, can beefficiently sent over a radio (wireless) interface that has a relativelysmall bandwidth.

A radio resource control (RRC) layer located at the lowest portion ofthe L3 is only defined in the control plane and controls logicalchannels, transport channels and the physical channels in relation tothe configuration, reconfiguration, and release of the radio bearers(RBs). Here, the RB signifies a service provided by the L2 for datatransmission between the terminal and the UTRAN.

As illustrated in FIG. 3(a), the RLC and MAC layers (terminated in aneNB 20 on the network side) may perform functions such as scheduling,automatic repeat request (ARQ), and hybrid automatic repeat request(HARQ). The PDCP layer (terminated in eNB 20 on the network side) mayperform the user plane functions such as header compression, integrityprotection, and ciphering.

As illustrated in FIG. 3(b), the RLC and MAC layers (terminated in aneNodeB 20 on the network side) perform the same functions for thecontrol plane. As illustrated, the RRC layer (terminated in an eNB 20 onthe network side) may perform functions such as broadcasting, paging,RRC connection management, RB control, mobility functions, and UEmeasurement reporting and controlling. The NAS control protocol(terminated in the MME of gateway 30 on the network side) may performfunctions such as a SAE bearer management, authentication, LTE_IDLEmobility handling, paging origination in LTE_IDLE, and security controlfor the signaling between the gateway and UE 10.

The RRC state may be divided into two different states such as aRRC_IDLE and a RRC_CONNECTED. In RRC_IDLE state, the UE 10 may receivebroadcasts of system information and paging information while the UEspecifies a discontinuous reception (DRX) configured by NAS, and the UEhas been allocated an identification (ID) which uniquely identifies theUE in a tracking area and may perform PLMN selection and cellre-selection. Also, in RRC_IDLE state, no RRC context is stored in theeNB.

In RRC_CONNECTED state, the UE 10 has an E-UTRAN RRC connection and acontext in the E-UTRAN, such that transmitting and/or receiving datato/from the network (eNB) becomes possible. Also, the UE 10 can reportchannel quality information and feedback information to the eNB.

In RRC_CONNECTED state, the E-UTRAN knows the cell to which the UE 10belongs. Therefore, the network can transmit and/or receive data to/fromUE 10, the network can control mobility (handover and inter-radio accesstechnologies (RAT) cell change order to GSM EDGE radio access network(GERAN) with network assisted cell change (NACC)) of the UE, and thenetwork can perform cell measurements for a neighboring cell.

In RRC_IDLE state, the UE 10 specifies the paging DRX cycle.Specifically, the UE 10 monitors a paging signal at a specific pagingoccasion of every UE specific paging DRX cycle.

The paging occasion is a time interval during which a paging signal istransmitted. The UE 10 has its own paging occasion.

A paging message is transmitted over all cells belonging to the sametracking area. If the UE 10 moves from one tracking area to anothertracking area, the UE will send a tracking area update message to thenetwork to update its location.

FIG. 4 shows an example of structure of a physical channel.

The physical channel transfers signaling and data between layer L1 of aUE and eNB. As illustrated in FIG. 4, the physical channel transfers thesignaling and data with a radio resource, which consists of one or moresub-carriers in frequency and one more symbols in time.

One sub-frame, which is 1 ms in length, consists of several symbols. Theparticular symbol(s) of the sub-frame, such as the first symbol of thesub-frame, can be used for downlink control channel (PDCCH). PDCCHscarry dynamic allocated resources, such as PRBs and modulation andcoding scheme (MCS).

A transport channel transfers signaling and data between the L1 and MAClayers. A physical channel is mapped to a transport channel.

Downlink transport channel types include a broadcast channel (BCH), adownlink shared channel (DL-SCH), a paging channel (PCH) and a multicastchannel (MCH). The BCH is used for transmitting system information. TheDL-SCH supports HARQ, dynamic link adaptation by varying the modulation,coding and transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The PCH is used for paging a UE. The MCH is usedfor multicast or broadcast service transmission.

Uplink transport channel types include an uplink shared channel (UL-SCH)and random access channel(s) (RACH). The UL-SCH supports HARQ anddynamic link adaptation by varying the transmit power and potentiallymodulation and coding. The UL-SCH also may enable the use ofbeamforming. The RACH is normally used for initial access to a cell.

The MAC sublayer provides data transfer services on logical channels. Aset of logical channel types is defined for different data transferservices offered by MAC. Each logical channel type is defined accordingto the type of information transferred.

Logical channels are generally classified into two groups. The twogroups are control channels for the transfer of control planeinformation and traffic channels for the transfer of user planeinformation.

Control channels are used for transfer of control plane informationonly. The control channels provided by MAC include a broadcast controlchannel (BCCH), a paging control channel (PCCH), a common controlchannel (CCCH), a multicast control channel (MCCH) and a dedicatedcontrol channel (DCCH). The BCCH is a downlink channel for broadcastingsystem control information. The PCCH is a downlink channel thattransfers paging information and is used when the network does not knowthe location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by MAC include a dedicated trafficchannel (DTCH) and a multicast traffic channel (MTCH). The DTCH is apoint-to-point channel, dedicated to one UE for the transfer of userinformation and can exist in both uplink and downlink. The MTCH is apoint-to-multipoint downlink channel for transmitting traffic data fromthe network to the UE.

Uplink connections between logical channels and transport channelsinclude a DCCH that can be mapped to UL-SCH, a DTCH that can be mappedto UL-SCH and a CC CH that can be mapped to UL-SCH. Downlink connectionsbetween logical channels and transport channels include a BCCH that canbe mapped to BCH or DL-SCH, a PCCH that can be mapped to PCH, a DCCHthat can be mapped to DL-SCH, and a DTCH that can be mapped to DL-SCH, aMCCH that can be mapped to MCH, and a MTCH that can be mapped to MCH.

The specification of a home eNB (HeNB) is currently ongoing in 3GPP LTE.It may be referred to Paragraph 4.6.1 of 3GPP (3rd generationpartnership project) TS 36.300 V10.2.0 (2010-12). The HeNB is a smallbase station designed for use in residential or small businessenvironment. The HeNB may be a femto cell. The HeNB is short range abouttens of meter, installed by the consumer for better indoor voice anddata reception.

FIG. 5 shows logical architecture of an E-UTRAN HeNB.

Referring to FIG. 5, a HeNB 50 may be connected with an EPC 60 throughan S1 interface. A HeNB gateway (55, HeNB GW) may be deployed betweenthe HeNB 50 and the EPC 60 to allow the S1 interface and to scale tosupport a large number of HeNBs. The HeNB GW 55 serves as a concentratorfor the C(control)-Plane, specifically the S1-MME interface. The S1-Uinterface from the HeNB 50 may be terminated at the HeNB GW 55, or adirect logical U(user)-Plane connection between HeNB 50 and S-GW 56 maybe used. The S1 interface may be defined as the interface between theHeNB GW 55 and the core network, between the HeNB 50 and the HeNB GW 55,between the HeNB 50 and the core network, and between the eNB and thecore network. Also, the HeNB GW 55 appears to the MME as an eNB. TheHeNB GW 55 appears to the HeNB as an MME. The S1 interface between theHeNB 50 and the EPC 60 is the same whether the HeNB 50 is connected tothe EPC 60 via a HeNB GW 55 or not.

Inter-cell interference coordination (ICIC) has the task to manage radioresources such that inter-cell interference is kept under control. TheICIC mechanism includes a frequency domain component and time domaincomponent. The preferred ICIC method may be different in the uplink anddownlink.

Meanwhile, the 3GPP LTE rel-8 (hereinafter, rel-8) and the 3GPP LTErel-10 (hereinafter, rel-10) ICIC mechanisms have been defined forintra-carrier cases. The rel-8 ICIC mechanism is designed for macrocell-only scenario. The Rel-10 ICIC mechanism is designed for scenariosof a macro cell and a femto cell as well as a macro cell and a picocell. Now for 3GPP LTE rel-11, the method of autonomous interferencemanagement in a heterogeneous network (HetNet) with the mixture ofdifferent cell types and without tight synchronization requirements isregarded as a next step of further development for the optimal use ofavailable frequency assets.

It is expected that the HetNet deployments in 3GPP LTE rel-11 basicallyassume that multiple carriers are used. On the other hand, 3GPP LTErel-10 uses single carrier. Therefore, when the ICIC mechanism isapplied to the HetNet deployments in 3GPP LTE rel-11, there might be afew of considerations.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for selecting acarrier in a wireless communication system. The present inventionprovides a method for a pico eNB and a home eNodeB (HeNB) selecting acarrier in a heterogeneous network (HetNet).

In an aspect, a method for selecting, by a pico eNodeB, a carrier in awireless communication system is provided. The method includestransmitting a carrier information request message including a requestof information on carriers used by a macro eNB, receiving a carrierinformation response message as a response of the carrier informationrequest message, the carrier information response message including theinformation on carriers used by the macro eNB, and selecting a primarycell (PCell) of the pico eNB based on the received information oncarriers used by the macro eNB.

The carrier information request message may be transmitted to the macroeNB through a direct X2 interface, and the carrier information responsemessage may be received from the macro eNB through the direct X2interface.

The carrier information request message or the carrier informationresponse message may be included in one of a resource status requestmessage, resource status response message, resource status updatemessage and load information.

The carrier information request message may be transmitted to the macroeNB directly during a direct X2 setup procedure, and the carrierinformation response message may be received from the macro eNB directlyduring the direct X2 setup procedure.

The carrier information request message may be included in an X2 setuprequest message, and the carrier information response message may beincluded in an X2 setup response message which is a response of the X2setup request message.

The information on carriers used by the macro eNB may indicate whichcarrier is mainly used as a PCell by the macro eNB.

The information on carriers used by the macro eNB may indicate whichother carrier is used as a secondary cell (Scell) by the macro eNB.

The method may further include measuring a reference signal receivedfrom the macro eNB.

The carrier information request message may be transmitted to a mobilitymanagement entity (MME) through an S1 interface, and the carrierinformation response message may be received from the MME through the S1interface.

The carrier information request message may be transmitted to a MMEduring an S1 setup procedure, and the carrier information responsemessage may be received from the MME during the S1 setup procedure.

In another aspect, a pico eNodeB for selecting a carrier in a wirelesscommunication system is provided. The pico eNB includes a radiofrequency (RF) unit for transmitting or receiving a radio signal, and aprocessor, operatively coupled to the RF unit, and configured fortransmitting a carrier information request message including a requestof information on carriers used by a macro eNB, receiving a carrierinformation response message as a response of the carrier informationrequest message, the carrier information response message including theinformation on carriers used by the macro eNB, and selecting a PCell ofthe pico eNB based on the received information on carriers used by themacro eNB.

In another aspect, a method for selecting, by a home eNodeB (HeNB), acarrier in a wireless communication system is provided. The methodincludes transmitting a carrier information request message including arequest of information on carriers used by a macro eNB to a HeNB gateway(GW), receiving a carrier information response message as a response ofthe carrier information request message from the HeNB GW, the carrierinformation response message including the information on carriers usedby the macro eNB, and selecting a PCell of the HeNB based on thereceived information on carriers used by the macro eNB.

The carrier information request message may be transmitted to the HeNBGW through an indirect X2 interface, and the carrier informationresponse message may be received from the HeNB GW through the indirectX2 interface.

The carrier information request message may be transmitted to the HeNBGW during an indirect X2 setup procedure, and the carrier informationresponse message may be received from the HeNB during the indirect X2setup procedure.

The carrier information request message may be included in an X2 setuprequest message, and the carrier information response message may beincluded in an X2 setup response message which is a response of the X2setup request message.

Automatic self carrier selecting mechanism without the need for priornetwork planning can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows network structure of an evolved universal mobiletelecommunication system (E-UMTS). The E-UMTS may be also referred to asan LTE system.

FIG. 2 shows architecture of a typical E-UTRAN and a typical EPC.

FIG. 3 shows a user-plane protocol and a control-plane protocol stackfor the E-UMTS.

FIG. 4 shows an example of structure of a physical channel.

FIG. 5 shows logical architecture of an E-UTRAN HeNB.

FIG. 6 shows an example of user equipments (UEs) in a HetNet.

FIG. 7 shows an example of proposed method of selecting a carrier in aHetNet according to an embodiment of the present invention.

FIG. 8 shows another example of proposed method of selecting a carrierin a HetNet according to an embodiment of the present invention.

FIG. 9 shows another example of proposed method of selecting a carrierin a HetNet according to an embodiment of the present invention.

FIG. 10 shows another example of proposed method of selecting a carrierin a HetNet according to an embodiment of the present invention.

FIG. 11 shows another example of proposed method of selecting a carrierin a HetNet according to an embodiment of the present invention.

FIG. 12 shows another example of proposed method of selecting a carrierin a HetNet according to an embodiment of the present invention.

FIG. 13 is a block diagram showing wireless communication system toimplement an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is an evolution of IEEE 802.16e, and provides backwardcompatibility with an IEEE 802.16-based system. The UTRA is a part of auniversal mobile telecommunication system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of anevolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA indownlink and uses the SC-FDMA in uplink. LTE-advance (LTE-A) is anevolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However,technical features of the present invention are not limited thereto.

To meet the targets set by 3GPP LTE-A, e.g., bandwidth up to 100 MHz,peak data rates up to 1 Gbps in DL and peak data rates up to 500 Mbps inUL, carrier aggregation (CA) concept is introduced. In the CA, two ormore component carriers (CCs) are aggregated in order to support widertransmission bandwidths up to 100 MHz. A UE may simultaneously receiveor transmit on one or multiple CCs depending on its capabilities. Thatis, a rel-10 UE with reception and/or transmission capabilities for theCA can simultaneously receive and/or transmit on multiple CCscorresponding to multiple serving cells. A Rel-8/9 UE can receive on asingle CC and transmit on a single CC corresponding to one serving cellonly. The CA is supported for both contiguous and non-contiguous CCs. Itis possible to configure a UE to aggregate a different number of CCsoriginating from the same eNB and of possibly different bandwidths inthe UL and the DL. That is, the number of DL CCs that can be configureddepends on the DL aggregation capability of the UE. The number of UL CCsthat can be configured depends on the UL aggregation capability of theUE.

When the CA concept is applied to the scenarios of pico eNB (or homeeNodeB (HeNB)) deployment, the pico eNB (or HeNB) can operate via a setof allowed carriers configured by operators. The basic principle is thateach cell should at least select one active primary carrier. That is, incase that a new pico eNB (or HeNB) is switched on, it shall start byselecting one carrier from the available carriers as its primarycarrier. However, due to the lack of synchronization requirementsbetween a macro eNB and a pico eNB (or HeNB), the interference relatedproblems can happen between the macro eNB and the newly deployed picoeNB (or HeNB). For example, the newly deployed pico eNB (or HeNB) mayselect one carrier which is used by the macro eNB as its primary carrierfrom the available carriers. Thus, some enhancements are needed for themethod of carrier selection in a heterogeneous network (HetNet)environment.

FIG. 6 shows an example of user equipments (UEs) in a HetNet.

Referring to FIG. 6, UEs close to a macro eNB exist (FIG. 6-(a)). Also,UEs closes to a pico eNB exist (FIG. 6-(b)). Also, UEs that are servedby the pico eNB while still far away from the pico eNB exist (FIG.6-(c)). In this case, these UEs will in fact suffer from a stronginterference from the macro eNB, which needs to be mitigated with theICIC mechanism, in the time-domain or frequency-domain or incombination. More specifically, in the HetNet deployment scenario, aprimary cell (PCell) is used for control/data part and a secondary cell(SCell) is used for data part with the aid of cross carrier scheduling.If the same carrier frequency is assigned for a macro UE and a pico eNBUE as their PCell, the interference on a physical downlink controlchannel (PDCCH) will be high. This is because the pico eNB is typicallylocated within the coverage of the macro eNB, thus, it would bebeneficial that the macro eNB and the pico eNB should configure theirown PCell using different carrier. In such scenario, providing inter-eNBassistance can be beneficial to optimize the selection of resourcesprotected from interference, while mitigating interference withavailable ICIC mechanisms for those UEs.

There are several ways to resolve the problems mentioned above.Hereinafter, various examples of the proposed method for selecting acarrier in a HetNet according to the present invention are described.Basically, it is assumed that the newly deployed pico eNB (or HeNB) maymeasure a reference signal from a macro eNB when it is powered on.

FIG. 7 shows an example of proposed method of selecting a carrier in aHetNet according to an embodiment of the present invention. This case isfor the scenario where the macro eNB and the HeNB cannot setup thedirect X2 interface between them.

Referring to FIG. 7, the newly deployed HeNB obtains the informationrequired for carrier selection via the X2 setup procedure between theHeNB and the HeNB GW with the aid of the HeNB GW. Here, the HeNB isready to first select the PCell.

At step S100, the HeNB transmits an X2 setup request message to the HeNBGW. The X2 setup request message may request the information on carriersused by the macro eNB by triggering the X2 setup procedure. The X2 setuprequest message may include carrier information request indication IE(information element) to obtain the information on the carriers used bythe macro eNB received through the reference signal. The carrierinformation request indication IE may be added either as a member IE ofneighbor information IE, which is the same format as described in the X2setup procedure, or as a separate IE.

At step S110, the HeNB GW transmits a carrier information requestmessage to the macro eNB. The carrier information request message mayinclude the carrier information request indication IE included in the X2setup request message.

At step S120, the macro eNB transmits a carrier information responsemessage to the HeNB GW as a response of the carrier information requestmessage. The carrier information response message may include carrierinformation response indication IE for the carriers of served cells. Thecarrier information response indication IE may indicates which carrieris mainly used as a PCell by the macro eNB and which other carrier(s) is(are) used as a SCell(s) by the macro eNB. The carrier informationresponse indication IE may be added either as a member IE of served cellinformation IE, which is the same format as described in the X2 setupprocedure, or as a separate IE.

At step S130, the HeNB GW transmits an X2 setup response message to theHeNB as a response of the X2 setup request message. The X2 setupresponse message may include the carrier information response indicationIE included in the carrier information response message.

When the HeNB receives the X2 setup response message from the HeNB GW,the HeNB may autonomously select its PCell based on the receivedinformation for mitigating the interference between itself and theneighbor macro eNB. In this way, the coordinated/uncoordinateddeployment of HeNB will benefit from having support of automatic carrierselection method.

FIG. 8 shows another example of proposed method of selecting a carrierin a HetNet according to an embodiment of the present invention. Thiscase is also for the scenario where the macro eNB and the HeNB cannotsetup the direct X2 interface between them. This example may beperformed after the indirect X2 interface is setup between the newlydeployed HeNB and the HeNB GW.

Referring to FIG. 8, the newly deployed HeNB obtains the informationrequired for carrier selection via a carrier information exchangeprocedure between the HeNB and the macro eNB with the aid of the HeNBGW. Here, the HeNB is ready to first select the PCell.

At step S200, the HeNB transmits a carrier information request messagemessage to the HeNB GW. The carrier information request message mayrequest the information on carriers used by the macro eNB by triggeringthe carrier information exchange procedure. The carrier informationrequest message may include carrier information request indication IE toobtain the information on the carriers used by the macro eNB receivedthrough the reference signal. The carrier information request indicationIE may be added either as a member IE of neighbor information IE, whichis the same format as described in the X2 setup procedure, or as aseparate IE.

At step S210, the HeNB GW forwards the carrier information requestmessage to the macro eNB.

At step S220, the macro eNB transmits a carrier information responsemessage to the HeNB GW as a response of the carrier information requestmessage. The carrier information response message may include carrierinformation response indication IE for the carriers of served cells. Thecarrier information response indication IE may indicates which carrieris mainly used as a PCell by the macro eNB and which other carrier(s) is(are) used as a SCell(s) by the macro eNB. The carrier informationresponse indication IE may be added either as a member IE of served cellinformation IE, which is the same format as described in the X2 setupprocedure, or as a separate IE.

At step S230, the HeNB GW forwards the carrier information responsemessage to the HeNB.

When the HeNB receives the carrier information response message from theHeNB GW, the HeNB may autonomously select its PCell based on thereceived information for mitigating the interference between itself andthe neighbor macro eNB. In this way, the coordinated/uncoordinateddeployment of HeNB will benefit from having support of automatic carrierselection method.

FIG. 9 shows another example of proposed method of selecting a carrierin a HetNet according to an embodiment of the present invention. Thiscase is also for the scenario where the macro eNB and the HeNB cannotsetup the direct X2 interface between them.

Referring to FIG. 9, the newly deployed HeNB obtains the informationrequired for carrier selection via the S1 setup procedure between theHeNB and the MME with the aid of the MME. Here, the HeNB is ready tofirst select the PCell.

At step S300, the HeNB transmits an S1 setup request message to the MME.The S1 setup request message may request the information on carriersused by the macro eNB by triggering the S1 setup procedure. The S1 setuprequest message may include carrier information request indication IE toobtain the information on the carriers used by the macro eNB receivedthrough the reference signal. The carrier information request indicationIE may be added either as a member IE of neighbor information IE, whichis the same format as described in the X2 setup procedure, or as aseparate IE.

At step S310, the MME transmits a carrier information request message tothe macro eNB. The carrier information request message may include thecarrier information request indication IE included in the S1 setuprequest message.

At step S320, the macro eNB transmits a carrier information responsemessage to the MME as a response of the carrier information requestmessage. The carrier information response message may include carrierinformation response indication IE for the carriers of served cells. Thecarrier information response indication IE may indicates which carrieris mainly used as a PCell by the macro eNB and which other carrier(s) is(are) used as a SCell(s) by the macro eNB. The carrier informationresponse indication IE may be added either as a member IE of served cellinformation IE, which is the same format as described in the X2 setupprocedure, or as a separate IE.

At step S330, the MME transmits an S1 setup response message to the HeNBas a response of the S1 setup request message. The S1 setup responsemessage may include the carrier information response indication IEincluded in the carrier information response message.

When the HeNB receives the S1 setup response message from the MME, theHeNB may autonomously select its PCell based on the received informationfor mitigating the interference between itself and the neighbor macroeNB. In this way, the coordinated/uncoordinated deployment of HeNB willbenefit from having support of automatic carrier selection method.

FIG. 10 shows another example of proposed method of selecting a carrierin a HetNet according to an embodiment of the present invention. Thiscase is also for the scenario where the macro eNB and the HeNB cannotsetup the direct X2 interface between them. This example may beperformed after the S1 interface is setup between the newly deployedHeNB and the MME.

Referring to FIG. 10, the newly deployed HeNB obtains the informationrequired for carrier selection via a carrier information exchangeprocedure between the HeNB and the macro eNB with the aid of the MME.Here, the HeNB is ready to first select the PCell.

At step S400, the HeNB transmits a carrier information request messageto the MME. The carrier information request message may request theinformation on carriers used by the macro eNB by triggering the carrierinformation exchange procedure. The carrier information request messagemay include carrier information request indication IE to obtain theinformation on the carriers used by the macro eNB received through thereference signal. The carrier information request indication IE may beadded either as a member IE of neighbor information IE, which is thesame format as described in the X2 setup procedure, or as a separate IE.

At step S410, the MME forwards the carrier information request messageto the macro eNB.

At step S420, the macro eNB transmits a carrier information responsemessage to the MME as a response of the carrier information requestmessage. The carrier information response message may include carrierinformation response indication IE for the carriers of served cells. Thecarrier information response indication IE may indicates which carrieris mainly used as a PCell by the macro eNB and which other carrier(s) is(are) used as a SCell(s) by the macro eNB. The carrier informationresponse indication IE may be added either as a member IE of served cellinformation IE, which is the same format as described in the X2 setupprocedure, or as a separate IE.

At step S430, the MME forwards the carrier information response messageto the HeNB.

When the HeNB receives the carrier information response message from theMME, the HeNB may autonomously select its PCell based on the receivedinformation for mitigating the interference between itself and theneighbor macro eNB. In this way, the uncoordinated deployment of HeNBwill benefit from having support of automatic carrier selection method.

The examples described in FIG. 9 and FIG. 10 assume that the presentinvention is applied in case of the HeNB is deployed. However, thepresent invention is not limited thereto. The present invention may beapplied in case of a pico eNB is deployed. That is, the HeNB describedin FIG. 9 to FIG. 12 can be replaced with the pico eNB.

FIG. 11 shows another example of proposed method of selecting a carrierin a HetNet according to an embodiment of the present invention. Thiscase is for the scenario where the macro eNB and the pico eNB (or HeNB)can setup the direct X2 interface between them.

Referring to FIG. 11, the newly deployed pico eNB (or HeNB) obtains theinformation required for carrier selection via the X2 setup proceduredirectly between the pico eNB (or HeNB) and the macro eNB. Here, thepico eNB (or HeNB) is ready to first select the PCell.

At step S500, the pico eNB (or HeNB) transmits an X2 setup requestmessage to the macro eNB. The X2 setup request message may request theinformation on carriers used by the macro eNB by triggering the X2 setupprocedure. The X2 setup request message may include carrier informationrequest indication IE to obtain the information on the carriers used bythe macro eNB received through the reference signal. The carrierinformation request indication IE may be added either as a member IE ofneighbor information IE, which is the same format as described in the X2setup procedure, or as a separate IE.

At step S510, the macro eNB transmits an X2 setup response message tothe pico eNB (or HeNB) as a response of the X2 setup request message.The X2 setup response message may include carrier information responseindication IE for the carriers of served cells. The carrier informationresponse indication IE may indicates which carrier is mainly used as aPCell by the macro eNB and which other carrier(s) is (are) used as aSCell(s) by the macro eNB. The carrier information response indicationIE may be added either as a member IE of served cell information IE,which is the same format as described in the X2 setup procedure, or as aseparate IE.

When the pico eNB (or HeNB) receives the X2 setup response message fromthe macro eNB, the pico eNB (or HeNB) may autonomously select its PCellbased on the received information for mitigating the interferencebetween itself and the neighbor macro eNB. In this way, the deploymentof pico eNB (or HeNB) will benefit from having support of automaticcarrier selection method.

FIG. 12 shows another example of proposed method of selecting a carrierin a HetNet according to an embodiment of the present invention. Thiscase is also for the scenario where the macro eNB and the pico eNB (orHeNB) can setup the direct X2 interface between them. This example maybe performed after the direct X2 interface is setup between the newlydeployed pico eNB (or HeNB) and the macro eNB.

Referring to FIG. 12, the newly deployed pico eNB (or HeNB) obtains theinformation required for carrier selection via the carrier informationexchange procedure directly between the pico eNB (or HeNB) and the macroeNB. Here, the pico eNB (or HeNB) is ready to first select the PCell.

At step S600, the pico eNB (or HeNB) transmits a carrier informationrequest message to the macro eNB. The carrier information requestmessage may request the information on carriers used by the macro eNB bytriggering the carrier information exchange procedure. The carrierinformation request message may include carrier information requestindication IE to obtain the information on the carriers used by themacro eNB received through the reference signal. The carrier informationrequest indication IE may be added either as a member IE of neighborinformation IE, which is the same format as described in the X2 setupprocedure, or as a separate IE.

At step S610, the macro eNB transmits a carrier information responsemessage to the pico eNB (or HeNB) as a response of the carrierinformation request message. The carrier information response messagemay include carrier information response indication IE for the carriersof served cells. The carrier information response indication IE mayindicates which carrier is mainly used as a PCell by the macro eNB andwhich other carrier(s) is (are) used as a SCell(s) by the macro eNB. Thecarrier information response indication IE may be added either as amember IE of served cell information IE, which is the same format asdescribed in the X2 setup procedure, or as a separate IE.

When the pico eNB (or HeNB) receives the carrier information responsemessage from the macro eNB, the pico eNB (or HeNB) may autonomouslyselect its PCell based on the received information for mitigating theinterference between itself and the neighbor macro eNB. In this way, thedeployment of pico eNB (or HeNB) will benefit from having support ofautomatic carrier selection method.

The carrier information request/response messages mentioned above arethe simple examples of messages exchanged between the macro eNB and thepico eNB (or HeNB) to achieve the interference mitigation between them.That is, the carrier information request/response indications describedin the above examples may be substituted with the existing X2 messages,e.g., resource status request/response/update message, load informationmessage, etc. FIG. 13 is a block diagram showing wireless communicationsystem to implement an embodiment of the present invention.

A pico eNB or HeNB 800 includes a processor 810, a memory 820, and an RF(radio frequency) unit 830. The processor 810 may be configured toimplement proposed functions, procedures, and/or methods in thisdescription. Layers of the radio interface protocol may be implementedin the processor 810. The memory 820 is operatively coupled with theprocessor 810 and stores a variety of information to operate theprocessor 810. The RF unit 830 is operatively coupled with the processor810, and transmits and/or receives a radio signal.

A macro eNB 900 may include a processor 910, a memory 920 and a RF unit930. The processor 910 may be configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 910. The memory 920 is operatively coupled with the processor910 and stores a variety of information to operate the processor 910.The RF unit 930 is operatively coupled with the processor 910, andtransmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What has been described above includes examples of the various aspects.It is, of course, not possible to describe every conceivable combinationof components or methodologies for purposes of describing the variousaspects, but one of ordinary skill in the art may recognize that manyfurther combinations and permutations are possible. Accordingly, thesubject specification is intended to embrace all such alternations,modifications and variations that fall within the spirit and scope ofthe appended claims.

What is claimed is:
 1. A method for selecting, by a pico eNodeB, acarrier in a wireless communication system, the method comprising:measuring a reference signal received from a macro eNB when the picoeNodeB is powered on; transmitting a carrier information request messageincluding a request of information on carriers used by the macro eNB;receiving a carrier information response message as a response of thecarrier information request message, the carrier information responsemessage including the information on carriers used by the macro eNB;selecting, by the pico eNodeB, a primary cell (PCell) of the pico eNBautonomously based on the received information on carriers used by themacro eNB, and wherein the information on carriers used by the macro eNBindicates which carrier is mainly used as the PCell by the macro eNB andwhich other carrier is used as a secondary cell (Scell) by the macroeNB.
 2. The method of claim 1, wherein the carrier information requestmessage is transmitted to the macro eNB through a direct X2 interface,and wherein the carrier information response message is received fromthe macro eNB through the direct X2 interface.
 3. The method of claim 2,wherein the carrier information request message or the carrierinformation response message is included in one of a resource statusrequest message, resource status response message, resource statusupdate message and load information.
 4. The method of claim 1, whereinthe carrier information request message is transmitted to the macro eNBdirectly during a direct X2 setup procedure, and wherein the carrierinformation response message is received from the macro eNB directlyduring the direct X2 setup procedure.
 5. The method of claim 4, whereinthe carrier information request message is included in an X2 setuprequest message, and wherein the carrier information response message isincluded in an X2 setup response message which is a response of the X2setup request message.
 6. The method of claim 1, wherein the carrierinformation request message is transmitted to a mobility managemententity (MME) through an S1 interface, and wherein the carrierinformation response message is received from the MME through the S1interface.
 7. The method of claim 1, wherein the carrier informationrequest message is transmitted to a MME during an S1 setup procedure,and wherein the carrier information response message is received fromthe MME during the S1 setup procedure.
 8. A pico eNodeB for selecting acarrier in a wireless communication system, the pico eNB comprising: aradio frequency (RF) unit for transmitting or receiving a radio signal;and a processor, operatively coupled to the RF unit, that: measures areference signal received from a macro eNB when the pico eNodeB ispowered on; controls the RF unit to transmit a carrier informationrequest message including a request of information on carriers used bythe macro eNB; controls the RF unit to receive a carrier informationresponse message as a response of the carrier information requestmessage, the carrier information response message including theinformation on carriers used by the macro eNB; selects, by the pico eNB,a primary cell (PCell) of the pico eNB autonomously based on thereceived information on carriers used by the macro eNB, and wherein theinformation on carriers used by the macro eNB indicates which carrier ismainly used as the PCell by the macro eNB and which other carrier isused as a secondary cell (Scell) by the macro eNB.
 9. A method forselecting, by a home eNodeB (HeNB), a carrier in a wirelesscommunication system, the method comprising: measuring a referencesignal received from a macro eNB when the home eNodeB is powered on;transmitting a carrier information request message including a requestof information on carriers used by the macro eNB to a HeNB gateway (GW);receiving a carrier information response message as a response of thecarrier information request message from the HeNB GW, the carrierinformation response message including the information on carriers usedby the macro eNB; selecting, by the HeNB, a PCell of the HeNBautonomously based on the received information on carriers used by themacro eNB, and wherein the information on carriers used by the macro eNBindicates which carrier is mainly used as the PCell by the macro eNB andwhich other carrier is used as a secondary cell (Scell) by the macroeNB.
 10. The method of claim 9, wherein the carrier information requestmessage is transmitted to the HeNB GW through an indirect X2 interface,and wherein the carrier information response message is received fromthe HeNB GW through the indirect X2 interface.
 11. The method of claim9, wherein the carrier information request message is transmitted to theHeNB GW during an indirect X2 setup procedure, and wherein the carrierinformation response message is received from the HeNB during theindirect X2 setup procedure.
 12. The method of claim 11, wherein thecarrier information request message is included in an X2 setup requestmessage, and wherein the carrier information response message isincluded in an X2 setup response message which is a response of the X2setup request message.